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ABSTRACT: Seafloor Landslides in Regions of Gas Hydrate, a Global Change Perspective

Robert E. Kayen, H. J. Lee

Observations by marine scientists of the occurrence of seafloor landslides in regions of gas hydrate have been made at numerous localities around the world. Large excess pore-water pressures, which are likely to be generated during either a drop in sea level or an increase in bottom-water temperature as a result of decomposing gas hydrate, may have caused many of these slope instabilities.

A drop in glacial-eustatic sea level causes reduced total pressures acting on seafloor sediment. Normally, pore pressures within the sediment column dissipate sufficiently during a drop in sea level to maintain a nearly hydrostatic condition. However, in regions of marine gas hydrate, reduction of sea level initiates decomposition along the base of the gas hydrate which, in turn, causes the release of large volumes of gas into the sediment and creates high excess pore-fluid pressures. Similarly, temperature increase in the upper portion of a marine gas hydrate can lead to decomposition of the hydrate-lattice and the release of free gas. The excess pressures generated by decomposing gas hydrate reduce slope stability.

A quantitative approach was taken to predict both the condition of excess pressure generation at a gas hydrate boundary, and the relative stability of the overlying sediment column, for a variety of sediment types and slope geometries. Our studies indicate that unless pressures can be adequately vented away from the decomposing gas hydrate, slope failure is likely for many sediment types. These models give credence to the theory that global climate fluctuations, manifest in Pleistocene sea-level lowering events and interglacial bottom-water temperature increases, likely initiated seafloor landslides at many

locations around the world where gas hydrate is present in outer continental margin sediment.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990